1. Field of the Invention
Exemplary embodiments of the invention relate to a liquid crystal display and a method of driving the same capable of implementing a local dimming.
2. Discussion of the Related Art
A liquid crystal display has an increasing application range because of light-weight, thin, low-power consumption features. The liquid crystal display has been used for portable computers such as laptop computers, office automation apparatuses, audio/video devices, and indoor/outdoor advertisement displays. A transmissive type liquid crystal display which occupies all most liquid crystal display devices displays a desired picture by controlling an electrical field applied to liquid crystal layer to modulate light incident from a backlight unit. The backlight unit is mainly classified into a direct type and an edge type.
Picture quality of the liquid crystal display depends on contrast property. The method improving the picture quality by modulating light incident from the backlight unit has a limitation. In order to improve the contrast property, a backlight dimming control method which adjusts luminance of the backlight unit according to the picture has been variously attempted. The backlight dimming control method may reduce power consumption by adaptably adjusting the luminance of the backlight unit depending on an input picture. The backlight dimming control method includes a global dimming method entirely adjusting luminance of a display screen and a local dimming method locally adjusting luminance of the display screen. The global dimming method may improve dynamic contrast measured between a previous frame and a next frame but it is difficult to improve static contrast. On the other hand, the local dimming method may improve static contrast by locally controlling luminance of the display screen in one frame period.
The direct type backlight unit has a construction in which a plurality of optical sheets and a diffusion plate are disposed under the liquid crystal display panel and a plurality of light sources are disposed under the diffusion plate. Even though the direct type backlight unit implements the local dimming method because the plurality of light sources are disposed under the diffusion plate and can be independently controlled, it is difficult to reduce a thickness thereof. Accordingly, it causes a problem to make a slim design of the liquid crystal display difficult. The reason why the direct type backlight unit can not be made to a slim construction is a space which is necessarily formed between the light sources and the diffusion plate. The diffusion plate diffuses light incident from the light sources to make luminance of the display screen uniformly. In order to sufficiently diffuse light incident from the light sources, the space between the light sources and the diffusion plate should be sufficiently guaranteed. According to the trend requiring the slim liquid crystal display, the space between the light sources and the diffusion plate is narrowed in gradual, but it makes bright lines on the display screen to lower a luminance evenness of the display screen because the light sources are observed on the display screen when the light from the light sources can not be sufficiently diffused.
The edge type backlight unit has a construction in which a light source is arranged to face a side surface of a light guide plate and a plurality of optical sheets are disposed between a liquid crystal display panel and the light guide plate. The edge type backlight unit may be implemented to have a structure thinner than the direct type backlight unit. However, it is impossible to apply the local dimming method to the edge type backlight unit because the light source illustrates light to one side of the light guide plate and the light guide plate serves to convert spot light or line light into surface light. If the local dimming method is applied to the edge type backlight unit, a distortion is observed on the display screen because light and shade are generated on an undesired area of the display screen by going-straight property of light. Furthermore, it causes another problem to decrease an entire luminance of the display screen because the evenness of the surface luminance at different areas of the light guide plate are different according to distances between positons in the light guide plate and the light source.